[Iccrg] Re: [tcpm] ECN feedback discussion

[Michael Welzl]

Great idea, I'd love for this semantic shift to happen!


On Nov 7, 2012, at 2:10 PM, Scheffenegger, Richard wrote:

> Hi,
>
> I just wanted to keep a record of these interesting remarks on the  
> list, for further discussion.
>
> We discussed ECN both in TCPM and ICCRG, and this post is to start  
> the discussion on the working group lists.
>
> During the TCPM session, Matt Mathis made an interesting remark on  
> the microphone. To paraphrase (my understanding), current marking  
> schemes (RED, CoDel, PIE,…) assume that ECN marks get treated like  
> loss by the end systems.  Therefore, they employ a “low density”  
> marking scheme, with marks expected at an (average) rate of around  
> 3% or so at maximum.
>
> Alternative schemes, that start getting deployed at this time, have  
> very simple marking schemes in the network, and give more  
> information to the end systems for processing and reaction there. As  
> a side effect, these newer schemes may run as high as 100% marking  
> for certain periods (longer than a single flows RTT), so they could  
> be classified as “high density” marking scheme.
>
>
> Later on, Bob noted, that since ECN Nonce is virtually nonexistent  
> (I know only one stack with partial support), why not re-define  
> ECT(1) to be used by high density marking schemes, keeping ECT(0)  
> for low density schemes (as deployed today). For newer stacks, this  
> would allow an even more fine grained reaction to ECN marking levels…
>
> However, ECN security aspects (Nonce) and legacy uses (ECT(1) has  
> the same meaning for existing ECN stacks as ECT(0)) would not be  
> addressed, but then again, current ECN is also virtually not  
> deployed, according to recent studies.
>
> Of course, such a shift in the semantics of ECT(0) vs ECT(1) would  
> also need to have an impact on the future signaling  / feedback  
> scheme used for TCP (DCCP and SCTP would be able to cope already,  
> afaik).
>
> Best regards,
>
> Richard Scheffenegger
>
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